The present invention relates to an alignment verification system and in particular to a system for verifying that rails extending across a fixed span and movable span of a movable span railroad bridge are within an acceptable degree of misalignment.
Proper alignment of a moveable span with a fixed span of a moveable span railroad bridge, such as a swing span bridge or draw bridge, is important for railroad safety. Excessive misalignment of the rails on the moveable span with the rails on the fixed span as the train advances thereacross, could result in derailment of the train or excessive wear on the rails. Current federal railroad administration rules specify that trains should not be permitted to cross moveable span bridges if the rails on the moveable span are not aligned with the rails on the fixed span within 3/8 of an inch.
Mechanical systems have been developed for verifying that the moveable span has returned to a closed position in general alignment with the fixed span before permitting trains to pass thereacross. One such system is disclosed in U.S. Pat. No. 5,186,421. Such systems typically only detect misalignment in one plane, either vertically or horizontally. Further, existing systems do not permit relatively precise verification that the rails are within a fairly narrow range of misalignment. One limiting factor on the development of mechanical systems which might be capable of verifying whether the rails are within a narrow range of misalignment, is the severe pounding and vibration on the rails as a train passes thereacross. It is unlikely that a mechanical system mounted to the rails and adapted to measure or verify a relatively narrow range of misalignment could withstand the vibration or pounding generated by a train and remain effective.
There remains a need for a reliable system for verifying that the rails of a movable span of a moveable span bridge are within a relatively narrow range of misalignment with the rails of a fixed span thereof which can be used to control the travel of trains thereacross.